python异常处理

异常处理

异常就是程序运行时发生错误的信号，也就是我们常说的报错
报错分为两种
调试和错误
调试是指程序员在写代码的时候出现了错误，进行修改
错误是指程序在运行的过程中，我们哪方面没有考虑到，出现了错误
 
万能异常

try:
     a=1/0
except Exception as e:
     print(e)

结果是
division by zero

 
万能异常和其他异常相结合
万能异常放最下面

try:
	name
	import a
	a=1/0
except IndexError as e3:
	print(e3)
except NameError as e2:
	print(e2)
except SyntaxError as e:
	print(e)
except Exception as e1:
	print(e1）

 
else程序没有报错，就执行else里面的程序

try:
        a=1/1
except Exception as e1:
	print(e1)
else:
	print('执行else')

结果是
执行else

 
finally不管程序是否出错都会运行finally

try:
	name
	import a
	a=1/0
except IndexError as e3:
	print(e3)
except NameError as e2:
	print(e2)
except SyntaxError as e:
	print(e)
except Exception as e1:
	print(e1)
else:
	print('执行else')
finally:
	print('执行finally')

结果是
name 'name' is not defined
执行finally

 
raise主动抛出异常

try:
	a=1/0
except Exception:
	print('抛出异常')
	raise 

结果是
抛出异常
Traceback (most recent call last):
  File "C:\Users\Administrator\Desktop\test.py", line 2, in <module>
    a=1/0
ZeroDivisionError: division by zero

 
自定义异常

class EvaException(Exception):
	def __init__(self,msg):
		self.msg=msg


raise EvaException('这是一个自定义的错误')
结果是
Traceback (most recent call last):
  File "C:\Users\Administrator\Desktop\test.py", line 6, in <module>
    raise EvaException('这是一个自定义的错误')
__main__.EvaException: 这是一个自定义的错误